Most of the time I start at the beginning and finish at the end. I know that sounds facetious, but sometimes I discover the beginning isn’t, and the ending wasn’t.
But I intend to build the book, scene by scene, in the order the reader will eventually read it. While my brain can be all over the place, sliding backward and forward in the timeline of the novel with great ease, the creative muscle prefers the linear approach. It also annoys me to have text ahead of the insertion marker; I like to see the clean white space slowly fill with words.
If I do think of other scenes or I know a scene will be critical and I can see it vividly enough to want to record it, I go ahead and bang it onto the page, but it’s in another document. My novels are driven by the character arc, so it would be difficult to accurately write a late scene that reflects all the growth of the novel when I haven’t written those earlier scenes yet.
When I get to where the scene I’ve already written goes, I read what I wrote, but it’s usually so in need of revision and weaving into the existing story that I can’t use it by just cut and paste. The emotional epiphany or needed plot elements are there, but I write the whole scene fresh. It does go much faster because of what I already scrawled into a document, as rough or possibly inaccurate as that edition may be.
I treat old efforts the same way. By that I mean, if I have an old short story or piece of a novel I didn’t use, when I think I can use it, I read it and compose it again as opposed to editing it. Maybe I’m just a zippy typist, but I can read a bad sentence from ten years ago, fix it in my head and retype it faster than I can click and right-click to edit it.
Every once in a while, I will find a thought or theme in that hastily written future scene that I completely forgot about while merrily writing the earlier part of the book. That becomes a purely artistic call: do I get out the seam ripper and take apart the garment of the document to add the theme? Or do I trust that forgetting all about it means it wasn’t important to start with? More often than not, I get out the seam ripper. I’ll do it to fix an error (once, all the way back to page 3), or to incorporate an editor’s thoughts, so it seems like I ought to give myself the same effort.
So in summary I would say I think in a non-linear pattern, but I record and assemble the finished product with a linear discipline. Whether that reflects my personality, I’m not sure. As a Pisces with six planets in Pisces, I’m lucky not to be in orbit. My muse is the Pisces, but the writer’s legs touch the ground, even though sometimes she’s on tiptoes.